Sirius Black's Twin Sister
by Proud Ravenclaw Girl
Summary: Cassiopeia Lyra Black, Sirius Black's twin sister, was close to Sirius before they went to Hogwarts. Sorted into Slytherin and with the war waging on, she will have to figure out what she truly believes in and what side she will fight for. Either side leads to the betrayal of family she holds dear.
1. Chapter 1

Disclaimer: I do not own anything of the Harry Potter franchise that seems familiar.

Prologue

Christmas Break 1995

Most of Number Twelve Grimmauld Place's residents were having a gloomy Christmas with Mr. Weasley in the hospital. Harry Potter was exploring a part of the house he was not in the last time he was there. This part of the house seemed untouched by Mrs. Weasley's cleaning. He saw a door that had "Cassie's Room" carved into it. Curious, he turned the door knob and found it unlocked. Inside was a room decorated the way he would image a Slytherin girl would decorate it, a lot of green with elegant furniture.

"You know you aren't supposed to be in this part of the house," Sirius said from behind him. Sighing, he stepped into the room. "What's sad is we never found out whose side she was on. Voldemort did kill her personally but he was killed his own followers in the past."

"Who?" Harry asked.

"Cassiopeia Lyra Black, my younger twin sister. We were quite close before Hogwarts. She would have made an excellent Marauder. We grew more and more apart during our years at Hogwarts." Sirius walked out of the room into a room with his own name on it and closed the door behind him.

Harry took one last look at the room and walked out closing the door behind him. He went back to his and Ron's room where the pair of them played chess watched by Hermione, Ginny, and Crookshanks.

* * *

AN: This is a story I started years ago that I randomly decided to continue working on since I am having slight writer's block on my other story. Although, it has been less than half a year since I updated my other story which is not bad since I have gone almost a year without updating it before.

The rating might be a little extreme but the themes in this story do get quite dark.


	2. Chapter 2

Chapter One

1968

"SIRIUS! CASSIE! WHICH ONE OF YOU TURNED MY HAIR RED?" A seven-year-old Regulus yelled.

"If it was me, your hair would be a more unnatural color like blue!" An eight-year-old Cassie yelled back.

"SIRIUS!"

Sirius was laughing on his bed in his room. The door to his room was of course locked.

* * *

Summer 1971

"SHE DID WHAT!" Walburga Black yelled after reading the letter she was sent that morning from Druella Black. She withdrew her wand and went straight for the family tapestry room. Then preceded to curse the tapestry so the spot where Andromeda Black was shown now had a black spot.

Back in the dining room, Orion Black picked up the discarded letter to see what upset his wife so greatly. When he finished reading the letter, he sighed and passed the letter to his children to read. Sirius, Cassie, and Regulus read the letter with their eyes widening as they did so. No one dared to talk about the contents of the letter, about how Andromeda had run off and married a mudblood. They all remained silent throughout the rest of breakfast even when Mrs. Black returned.

* * *

September 1st, 1971

Both Sirius and Cassie had their trunks packed and were in the entrance.

"Cassiopeia, follow me. You and I are going to have a talk before you leave," Walburga Black informed her daughter. Gulping, Cassie followed her into the dining room. "I figured trying to talk sense into Sirius would be a waste of time and I hope I am not wasting time with you. Merlin forbid, Regulus being the only one of you three to turn out alright. Our family faced enough disgrace this past summer. You will be sorted into Slytherin or at least Ravenclaw. Either stop the pranks or stick to Gryffindors, blood traitors, and mudbloods _without_ getting caught. You will act like a perfect pureblood or you will regret it. Do I make myself clear?"

"Yes, Mother."

"Good."

Mrs. Black turned around and headed back to the entrance way with Cassie following her. Sirius and Cassie grabbed their trunks and they flooed to platform nine and three quarters.

"Remember to make the Black family proud," Mrs. Black told them before Sirius grabbed Cassie's hand and dragged her onto the train.

Sirius dragged her until they found an empty compartment on the train. Sirius lifted their trucks up into the ranks above the seats and they collapsed into their seats. Slowly, throughout the train ride, their compartment began to fill up with boys that their mother would disapprove of. Their names being James Potter, Remus Lupin, and Peter Pettigrew. James and Sirius were becoming fast friends while Cassie was looking more nervous.

Remus Lupin noticing how nervous Cassie looked asked, "Is something wrong?"

"Mother is not going to be too happy if she finds out who Sirius and I spent the train ride with. Especially after what happened with Cousin Andy this summer," Cassie replied.

"It will be alright, little sister," Sirius tells her in a reassuring voice while pulling her into a hug.

"But Mother is the type that would pull me out of school early and marry me off to some abusive old geezer just so I don't turn out like Cousin Andy," Cassie responded while slightly crying. The other occupants of their compartment looked slightly horrified by her answer.

"Language," Sirius reprimanded her. "If need be, I'll step in and take full responsibility. I won't let Mother do anything like that to you. Although, at least we know he would be rich. Mother won't settle for anyone who wasn't." Cassie gave her twin a playful swipe after his last comment with a small smile on her face. "There's that smile I was looking for."

"So," James started trying to break the thick tension that formed. "What house does everybody think they will get into? Personally, I am hoping to get into Gryffindor, the house of the brave."

"Almost every Black has been in Slytherin. I'm hoping for Gryffindor to rebel against my family," Sirius answered him. "Cassie here, though, even Mother admits she will probably end up in Ravenclaw. Biggest bookworm I know." Cassie's face turns bright red at Sirius' remark.

"Ravenclaw sounds nice," pipes out Remus from behind a book that no one noticed he had pulled out. "Although, I won't mind Gryffindor."

"Hufflepuff is probably the only house that would take me," Peter lamented.

The rest of the train ride was a lot cheerier and before they knew it, they arrived at Hogwarts.


	3. Chapter 3

Chapter 2

As they stepped off the train, there was a giant man calling out, "Firs' years! Firs' years over here! C'mon, follow me – any more firs' years? Mind yer step, now! Firs' years follow me!"

They followed the giant man down a dark, steep, narrow path. After a while of walking, the giant man called over his shoulder, "Ye' all get yer firs' sight o' Hogwarts in a sec, jus' round this bend here."

There was a loud "Oooooh" sound as many of the first years saw Hogwarts for the first time.

"No more'n four to a boat!" the giant man called, pointing to a fleet of little boats sitting in the water by the shore.

Sirius grabbed onto Cassie as they made their way for the boats. It was no surprise that James also ended up in the same boat. Though, Remus seemed to have beat Peter to their boat as he was the fourth occupant.

"Everyone in?" shouted the giant, who had a boat to himself. "Right then - FORWARD!" The boats started to move forward as one across the lake towards Hogwarts. As they approached the castle, the giant yelled, "Heads down!" The glided into a tunnel that led to an underground harbor. They climbed out of the boats, went through a passageway, and up a flight of stairs until they were in front of a large oak door. "Everyone here?" the giant asked before raising a gigantic fist and knocking three times on the castle door. The door opened to reveal a tall, back-haired, stern looking witch. "The firs' years, Professor McGonagall," the giant told her.

"Thank you, Hagrid. I will take them from here," Professor McGonagall replied. She then led the first years into a small, empty chamber to give them a welcoming speech. "Welcome to Hogwarts. The start-of-term banquet will begin shortly, but before you take your seats in the Great Hall, you will be sorted into your houses. The Sorting is a very important ceremony because, while you are here, your house will be something like your family within Hogwarts. You will have classes with the rest of your house, sleep in your house dormitory, and spend free time in your house common room.

"The four houses are called Gryffindor, Hufflepuff, Ravenclaw, and Slytherin. Each house has its own noble history and each has produced outstanding witches and wizards. While you are at Hogwarts, your triumphs will earn your house points, while any rule breaking will lose house points. At the end of the year, the house with the most points is awarded the house cup, a great honor. I hope each of you will be a credit to whichever house becomes yours.

"The Sorting Ceremony will take place in a few minutes in front of the rest of the school. I suggest you all smarten yourselves up as much as you can while you are waiting. I shall return when we are ready for you. Please wait quietly." She left the chamber.

Students started telling other students the creative ideas of how they heard the sorting happens. Cassie and Sirius gave each other assumed and knowing looks since they were some of the few who were actually told about the sorting hat before coming to Hogwarts.

Then one of the first years let out a shriek. About twenty ghosts had just streamed through the back wall. Pearly-white and slightly transparent, they glided across the room talking to one another and hardly glancing at the first years. They seemed to be arguing. What looked like a fat little monk was saying: "Forgive and forget, I say, we ought to give him a second chance –"

"My dear Friar, haven't we given Peeves all the chances he deserves? He gives us all a bad name and you know, he's not really even a ghost – I say, what are you all doing here?" A ghost wearing a ruff and tights had suddenly noticed the first years. Nobody answered.

"New students!" said the Fat Friar, smiling around at them. "About to be Sorted, I suppose?" A few people nodded mutely. "Hope to see you in Hufflepuff!" said the Friar. "My old house, you know."

"Move along now," said a sharp voice. "The Sorting Ceremony's about to start." Professor McGonagall had returned. One by one, the ghosts floated away through the opposite wall. "Now, form a line," Professor McGonagall told the first years, "and follow me."

They formed a line and followed Professor McGonagall into the Great Hall. She led them up to the front where she placed down a four-legged stool with the Sorting Hat on top of it. After a few moments, the Sorting Hat started to sing about the four houses. When the Sorting Hat finished its song, the whole hall burst into applause. The Sorting Hat bowed to each of the four tables and then became quite still again.

Professor McGonagall stepped forward and unrolled a long parchment. "When I call your name, you will put on the hat and sit on the stool to be sorted," she announced.

Cassie tuned out the sorting until she heard "Black, Cassiopeia" called. She walked forward, put the hat on her head, and sat down.

The hat then started speaking to her. _Hmm … well your family would be pleased you don't have many Gryffindor or Hufflepuff characteristics. Definitely a bookworm. Really, your ideal present is books?_ Cassie blushed red while being glad that the hat covered enough of her face that the blush could not be seen. _Yet, you want to be in Slytherin. All because you're scared that your brother will actually end up in Gryffindor and you hope that by you being placed in Slytherin will calm her down. Well, you do have the cunning and survival instincts of a Slytherin._ "SLYTHERIN!"

Cassie heard applause from the Slytherin table as she took off the Sorting Hat and placed in back on the stool. She glanced at Sirius and noticed he looked disappointed. She walked towards the Slytherin table and her smiling cousin, Narcissa Black.

"Cousin," Narcissa greeted her. "I see you will be joining us in Slytherin, and here everyone was thinking you would become a Ravenclaw."

At that moment, Cassie's fear was realized as the Sorting Hat called out "GRYFFINDOR!" for Sirius. Narcissa pulled her down onto the bench before a scene was made, and gave a look to the rest of the Slytherins as if telling them not to mention what just happened; a Black being sorted into Gryffindor.

The rest of the sorting passed in a blur for Cassie as she tried not to break down knowing that showing emotion in front of Slytherins was a fatal mistake.

* * *

AN: There are parts of the first book in this chapter. One, it is very hard to write the way Hagrid speaks. Two, why not add in McGonagall's welcome speech?


End file.
